1. Field of the Invention
The invention relates to the tire manufacture, and in particular, it deals with an apparatus for building covers for pneumatic tires.
The invention may be most advantageously used for layer assembly of large-size and giant tubeless tires with the diameter at rim seat from 25" to 69".
The invention may also be used for layer and combination assembly of truck and special-purpose multiply tires with several bands in the bead, both tube and tubeless.
2. Description of the Prior Art
In view of the present trend towards an increase in production of tubeless tires, especially large-size and giant tires, stringent requirements (first of all, tightness and mileage) are imposed upon their quality.
Known in the art is an apparatus for building pneumatic tire covers comprising a main tire-building drum and auxiliary tire-building drums which are mounted coaxially with one another. The auxiliary tire-building drums are mounted on supports having guide members. The apparatus comprises bead forming mechanisms, rotation drives for the main tire-building drum and for axial movement of the supports, and retainers. Each retainer comprises a pad made of an adhesive material and received in annular grooves and holes in the end face of each auxiliary drum on the side thereof facing the main tire-building drum (SU, A, 538898).
The above-described apparatus are deficient in that they cannot prevent the main and auxiliary tire-building drums from rotating relative to one another when they rotate together. This is due to the fact that friction forces developing at points of contact between the main and auxiliary tire-building drums owing to the provision of the adhesive retainers featuring frictional behavior are used for coupling the main and auxiliary tire-building drums to ensure their combined rotation. These friction forces cannot completely prevent the main and auxiliary tire-building drums from rotating relative to one another during their combined rotation, especially during the starting period of rotation when the cover parts are stitched since substantial inertia forces develop during this period owing to heavy mass and high speed of rotating parts, especially in building large-size tire covers.
Rotation of the main and auxiliary tire-building drums relative to one another results in a displacement of the material applied the main tire-building drum with respect to the material applied to the auxiliary tire-building drums so that folds and closed air voids are formed; a mechanical damage may occur to the sealing layer during the assembly of tubeless tires thus resulting in a cover defect that cannot be remedied.
The use of the retainers in the form of adhesive pads somewhat improves cohesion between the main and auxiliary drums, but it cannot completely rule out their relative rotation during combined rotation, especially in building large-size tire covers. In addition, in this case, during application of succeeding groups of material layers, when the drums are in contact with the material that has been applied to the main drum beforehand, the adhesive pads have a trend towards sticking to the material of the cover carcass so as to cause its damage when the auxiliary drums are retracted from the main drum.
Most similar to the invention is an apparatus for building pneumatic tire covers, comprising coaxial main and auxiliary tire-building drums. The auxiliary tire-building drums are mounted for rotation on supports which are installed on guide members. The apparatus also has a drive for rotation of the main tire-building drum and actuators for axially moving the supports of the auxiliary tire-building drums and a means for connecting the main tire-building drum to the auxiliary tire-building drum, comprising spring-biased pins rigidly secured to shoulders of the main tire-building drum and grooves provided in the end faces of the auxiliary tire-building drums facing towards the main tire-building drum. When the auxiliary tire-building drums are closed, the spring-biased pins are received in the grooves of the auxiliary tire-building drums (SU, A, 1183391). This construction prevents the main and auxiliary tire-building drums from rotating relative to one another when they rotate together during the assembly of the first groups of plies. However, the use of this apparatus would somewhat lower the tire building speed since the drums should be accurately positioned with respect to one another so that the spring-biased pins of the main tire-building drum could be received in the grooves in the end faces of the auxiliary tire-building drums, and this can only be achieved by a repeated step-by-step rotation of the main tire-building drum, first to bring the pins of the main tire-building drum in registry with the grooves of the first auxiliary tire-building drum, and then with the grooves of the second auxiliary tire-building drum. The final alignment of the pins with the grooves is effected by manually turning the auxiliary tire-building drums. The time spent for these manipulations results in a lower output of the apparatus. In addition, this apparatus cannot provide for a rigid engagement of the main tire-building drum with the auxiliary tire-building drums during the assembly of the second and succeeding groups of cover cord plies since the spring-biased pins of the main tire-building drum are covered with the material of the first group of plies and cannot be received in the grooves of the auxiliary tire-building drums so as to ensure their timed rotation.